Workpieces are typically held in place on a machining table with a vise having a fixed or “hard” jaw and a movable or “soft” jaw. A jaw is typically a device configured to hold a workpiece in place by applying a compressive force to the workpiece. The compressive force is generated by the linear motion of a soft jaw of the vise that is urged forward by the rotational movement of a screw drive or other force conversion mechanism to convert a torque to a linear motion. The screw drive provides a mechanical advantage to magnify force applied to the workpiece. However, as a compressive force is applied to the workpiece, the compressive force between the soft jaw and the screw drive may increase the friction therebetween, resulting in a rotational movement of the soft jaw and/or workpiece. A soft jaw may, therefore introduce variations in the placement of a workpiece when work on a first workpiece is complete and the first workpiece is removed and replaced with a second workpiece.
An example of a soft jaw for a machining vise is disclosed in U.S. Pat. No. 6,126,158, the disclosure of which is incorporated herein by reference in its entirety. A soft jaw may allow for the application of a compressive force to a workpiece with little to no transmission of a torque or other vertical movement to the workpiece. For example, a soft jaw may use an angled face between a jaw block and a drive block to apply a compressive force to the workpiece that is substantially linear and normal to the interface between the workpiece and the jaw block. The soft jaw applies a compressive force to the workpiece without altering the position of the workpiece (e.g., rotating or lifting the workpiece in the vise) to facilitate precision machining.
An automated machining or milling system, such as a computer numerical control (“CNC”) cutting machine, allows a machinist to load a template into the automated machining system and produce a part. The automated machining system can then use the same template to produce a plurality of identical parts. However, the accuracy of the automated machining system (i.e., the accuracy of the placement of the cuts in a workpiece) is at least partially dependent upon the precise position of the workpiece in the automated machining system. For example, when cutting a workpiece by hand, a machinist or woodworker will use the workpiece itself as the frame of reference for the cuts made in the workpiece. The reference frame for the movements of the automated machining system, in contrast is the chamber and/or table of the automated machining system. The position of the workpiece within the automated machining system is provided to the automated machining system by calibrating the automated machining system for each new workpiece that is placed in the automated machining system.
Calibrating the automated machining system between the cutting of each workpiece is a time-consuming process. The automated machine must of necessity be recalibrated each time an operator places additional workpieces in the machine to produce more pieces according to a previous template. Downtime of the automated machining system is financially costly as any downtime precludes time that commercially valuable pieces may be produced. A workpiece holder that allows for the minimization of calibration time is therefore desirable.